Among the numerous clasps for bands with length-adjusting devices, a clasp of the type indicated above has already been proposed in CH 668 353. One drawback of the adjustment device used in the clasp described in that document is that the tracks in which the two sliding members are engaged are simple openings passing through the side walls of the clasp cover. Such guide openings are there essentially to limit the amplitude of movement of the connecting member and to define its path, but they cannot guide it to move translationally. To this end, the connecting member is formed by a plate whose lateral edges slide against the side walls of the cover of the clasp. The device is therefore guided by a hybrid system which does not provide great accuracy and does not therefore ensure a smooth non-sticking sliding action.
Another drawback with that invention is that the members designed to change the position of the connecting member are the same members which control the opening and closing of the clasp. This means that there is no way of opening the clasp without changing the position of the connecting member and therefore losing the setting of the length. Clearly, this is a tiresome task for a user, every time the watch is taken off or put back on, as it may be several times in a day. Since furthermore this action is done by pushing towards each other two members which slide along an axis extending transversely relative to the band, and these members project from either side of the clasp, they can be operated unintentionally, even accidentally, which is of course undesirable.
Another clasp of this type is disclosed in JP 2000 279 217. In this clasp the length-adjusting device is independent of the opening and closing device but it does not eliminate the risk of unintentional or accidental operation of the pushbuttons used to control the adjustment device. Furthermore, this clasp has no real system for precisely guiding the translational movement of the connecting member.
CH 691 159 also presents a sliding adjustment member whose position is fixed by a screw. Such a system therefore requires a screwdriver and therefore cannot be adjusted unless one is in possession of a screwdriver that fits the screw. Considering the size of the screw, this usually requires a visit to a specialist.
Other prior clasps have length-adjusting devices using various movable racks whose position can be fixed using an immobilizing member, as described for example in U.S. Pat. No. 2,596,186. The disadvantage of such a device is that although for aesthetic reasons it is not possible to extend the rack from the ends of the clasp. The maximum length of adjustment simply cannot therefore extend to more than half the length of the clasp, which is manifestly not enough, especially for a clasp for a diving watch in particular, where the length of adjustment around the wrist with and without a diving suit must be more or less considerable, and in any event greater than half the length of a folding-arm clasp, which is itself limited by the size of the wrist.